Throwing an exception from a variable

Question

Using java, I want to do something like

try {
  someMethod();
} catch (Throwable x) {
  x.setMessage("Some comment " + x.getMessage());
  throw x;
}

That is, I do not know what "someMethod" will throw. Whatever it is, I want to add a message at the beginning of its message, and then throw the error. But Throwable does not have a setMessage() method.

I can do a Class<? extends Throwable> cls = x.getClass(); to get the class type, but I am not sure of the syntax. I can't do a throw new cls("Comment " + x.getMessage()); I am sure there must be a fairly simple way to do this, when you don't know the class of the throwable that is thrown.

Is there a reason not to use the more common pattern of catch (Throwable t) { throw new CustomExceptionOrSomething("Some comment", e); }? — mrmcgreg
– mrmcgreg, Commented Oct 8, 2018 at 19:47
It's not recommended to catch Throwable, since those could be JVM-level conditions (e.g., OutOfMemoryError). In almost all cases, you'd be better off catching Exception instead. — Mike Harris
– Mike Harris, Commented Oct 8, 2018 at 21:00

Makoto · Accepted Answer · 2018-10-08 19:49:08Z

2

Instead of catching Throwable (which is almost always a mistake), you can create a custom RuntimeException and wrap your caught exception in that.

public class MyException extends RuntimeException {
    public MyException(String message, Throwable cause) {
        super(message, cause);
    }
}

try {
    someMethod();
} catch(Exception e) {
    throw new MyException("A major error has occurred!", e);
}

answered Oct 8, 2018 at 19:49

Makoto

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3 Comments

shmosel Over a year ago

Or just wrap it directly in a RuntimeException.

Tony Over a year ago

Actually it occurs to me I need them to be assertion errors because I want the test (this is with Selenium) to continue even if a specific part fails. I have a List<AssertionError> errors = new ArrayList<>() to which I will add each error thrown and then throwIfNecessary() at the end

Oleg Ushakov Over a year ago

I will supplement the answer above, that you can also create your own custom exception, inheriting not only from RuntimeException but also from Exception class

ninja.coder · Accepted Answer · 2018-10-08 20:09:15Z

0

You can simply catch the Exception thrown by someMethod() and then re-throw it with the message you want.

Something like,

try {
   someMethod();
} catch(Exception ex) {
   /* Optional: Log Error */
   Logger.error(..., ex);
   throw new Exception("Error Occurred While Processing Request.", ex);
}

If you want you can also create and throw a checked exception as follows,

CustomException Class:

public class CustomException extends Exception {
    /* Optional: Add Serial UID */

    public CustomException(String message, Throwable cause) {
        super(message, cause);
    }

    public CustomException(Throwable cause) {
        super(cause);
    }
}

Code:

try {
   someMethod();
} catch(Exception ex) {
   /* Optional: Log Error */
   Logger.error(..., ex);
   throw new CustomException("Error Occurred While Processing Request.", ex);
}

edited Oct 8, 2018 at 20:09

answered Oct 8, 2018 at 20:03

ninja.coder

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1 Comment

Tony Over a year ago

I think I will try user2004685's suggestion since I can then add the exception to the array

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